Molecular dynamics simulation of carbon clusterization under martensite tempering

Further improvement of the properties of steel is impossible without understanding of the atomic-level processes that take place at the different stages of heat treatment. In this work a simulation of iron-carbon martensite was performed using the method of molecular dynamics with interatomic potential based on the embedded atom model (EAM). The observed diffusion of carbon on octahedral interstices at high temperatures (at several hundreds of $^\circ$C) causes the formation of short-range ordering of C atoms by way of periodical plain clusters divided by lattice regions, which almost do not contain carbon. We found that the cluster regions are orientated relative to iron lattice with (102) indices, what is consistent with the results of the experimental studies of the structures produced during martensite tempering at the stage of two-phase decomposition. The atomistic simulations results show that carbon clusterization causes the increasing of the lattice parameters relation c/a, both in the lattice regions where clusters are formed, and in the zones which do not contain any carbon atoms. The last fact is explained due to necessity of crystallographic coupling of these two zones. The thickness of the clusters turned out to equal 17 Å, and that of the regions not filled with carbon — 30 Å. During the simulation the total energy of modeling system decreases, and that can be considered as the reaction driving force with the value of 453,6 J/mole, which shows a qualitative agreement with other works.